Correction to: Proteomic characterization of adrenal gland embryonic development reveals early initiation of steroid metabolism and reduction of the retinoic acid pathway.

[This corrects the article DOI: 10.1186/s12953-015-0063-8.].

Proteomic characterization of adrenal gland embryonic development reveals early initiation of steroid metabolism and reduction of the retinoic acid pathway.

BACKGROUND: Adrenal glands are essential endocrine organs composed of two embryological distinct tissues. Morphological changes during their development are well described, but less understood with regard to their molecular mechanisms. To identify proteins and pathways, which drive the initial steps of the specification of the endocrine function of the adrenal gland, rat's adrenal glands were isolated at different embryonic days (E): E14, E16, E18, E19 and postnatal day 1 (P1). RESULTS: The alteration of the proteome during the stages E16, E19 and P1 was investigated by combining two dimensional gel electrophoresis and mass spectrometric analysis. Out of 594 excised protein spots, 464 spots were identified, resulting in 203 non-redundant proteins. The ontogenic classification of the identified proteins according to their molecular function resulted in 10 different categories, whereas the classification of their biological processes resulted in 19 different groups. This gives an insight into the complex mechanisms underlying adrenal gland development. Interestingly, the expression of retinoic acid pathway proteins was decreased during the development of the adrenal gland, suggesting that this pathway is only important at early stages. On the other hand, key proteins of the cholesterol synthesis increased their expression significantly at E19 revealing the initiation of the endocrine specialization of the adrenal glands. CONCLUSIONS: This study presents the first comprehensive wide proteome analysis of three different stages of embryonic adrenal gland development. The identified proteins, which were expressed in early stages of development, will shed light on the molecular mechanisms underlying embryonic development of the adrenal gland.

Photosensitizing effects of hypericin on head neck squamous cell carcinoma in vitro.

Clinical outcome of patients suffering from head neck squamous cell carcinomas is still poor due to recurrent disease and surgical limitations. There is still a demand for multimodality approaches and new therapeutic options. Hypericin is a promising phototoxic drug which was investigated for its effects on head neck squamous cell carcinoma cells in vitro. FaDu cells incubated with or without hypericin were illuminated (450-700 nm, 50,000 lx) for different time periods. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide- and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay were used to score metabolic and apoptotic activity. Even after the shortest illumination FaDu cells incubated with hypericin showed massive reduction of metabolism and excessive apoptosis. This was present even with the lowest hypericin concentration. Cells without hypericin or without illumination were not affected. These photosensitizing effects of hypericin could be suitable for clinical application and could lead to the development of an intraoperative photodynamic therapy of head neck squamous cell carcinomas.

Correlated optical and isotopic nanoscopy.

The isotopic composition of different materials can be imaged by secondary ion mass spectrometry. In biology, this method is mainly used to study cellular metabolism and turnover, by pulsing the cells with marker molecules such as amino acids labelled with stable isotopes ((15)N, (13)C). The incorporation of the markers is then imaged with a lateral resolution that can surpass 100 nm. However, secondary ion mass spectrometry cannot identify specific subcellular structures like organelles, and needs to be correlated with a second technique, such as fluorescence imaging. Here, we present a method based on stimulated emission depletion microscopy that provides correlated optical and isotopic nanoscopy (COIN) images. We use this approach to study the protein turnover in different organelles from cultured hippocampal neurons. Correlated optical and isotopic nanoscopy can be applied to a variety of biological samples, and should therefore enable the investigation of the isotopic composition of many organelles and subcellular structures.

NF-κB inhibitor targeted to activated endothelium demonstrates a critical role of endothelial NF-κB in immune-mediated diseases.

Activation of the nuclear transcription factor κB (NF-κB) regulates the expression of inflammatory genes crucially involved in the pathogenesis of inflammatory diseases. NF-κB governs the expression of adhesion molecules that play a pivotal role in leukocyte-endothelium interactions. We uncovered the crucial role of NF-κB activation within endothelial cells in models of immune-mediated diseases using a "sneaking ligand construct" (SLC) selectively inhibiting NF-κB in the activated endothelium. The recombinant SLC1 consists of three modules: (i) an E-selectin targeting domain, (ii) a Pseudomonas exotoxin A translocation domain, and (iii) a NF-κB Essential Modifier-binding effector domain interfering with NF-κB activation. The E-selectin-specific SLC1 inhibited NF-κB by interfering with endothelial IκB kinase 2 activity in vitro and in vivo. In murine experimental peritonitis, the application of SLC1 drastically reduced the extravasation of inflammatory cells. Furthermore, SLC1 treatment significantly ameliorated the disease course in murine models of rheumatoid arthritis. Our data establish that endothelial NF-κB activation is critically involved in the pathogenesis of arthritis and can be selectively inhibited in a cell type- and activation stage-dependent manner by the SLC approach. Moreover, our strategy is applicable to delineating other pathogenic signaling pathways in a cell type-specific manner and enables selective targeting of distinct cell populations to improve effectiveness and risk-benefit ratios of therapeutic interventions.

Release of matrix metalloproteinase-8 during physiological trafficking and induced mobilization of human hematopoietic stem cells.

Previous studies indicate that the release of proteases, including the gelatinase matrix metalloproteinase (MMP)-9, from mature granulocytes plays a crucial role in cytokine-induced hematopoietic stem and progenitor cell (HSPC) mobilization. However, studies with MMP-9-deficient mice revealed that HSPC mobilization was normal in these animals, suggesting that additional proteases must be active at clinically relevant cytokine concentrations. In the present study, we provide evidence that the collagenase MMP-8 is involved in stem cell mobilization. A rapid release of MMP-8 from isolated neutrophil granulocytes can be observed during an in vitro culture. During granulocyte colony-stimulating factor-induced HSPC mobilization, highly elevated serum concentrations of MMP-8 were observed on days 4 to 6 of the mobilization regimen, concomitantly with elevated MMP-9 serum levels and higher numbers of circulating CD34(+) cells. Elevated serum concentrations of both proteases were also found in umbilical cord blood serum. In functional assays, adhesion of HSPC to osteoblasts as an essential component of the endosteal stem cell niche is negatively influenced by MMP-8. The chemokine CXCL12, which is critically involved in stem cell trafficking, can be proteolytically processed by MMP-8 treatment. This degradation has a strong inhibitory influence on HSPC migration. Taken together, our data strongly suggest that MMP-8 can be directly involved in hematopoietic stem cell mobilization and trafficking.

Toll-like receptor activation reveals developmental reorganization and unmasks responder subsets of microglia.

The sentinel and immune functions of microglia require rapid and appropriate reactions to infection and damage. Their Toll-like receptors (TLRs) sense both as threats. However, whether activated microglia mount uniform responses or whether subsets conduct selective tasks is unknown. We demonstrate that murine microglia reorganize their responses to TLR activations postnatally and that this process comes with a maturation of TLR4-organized functions. Although induction of MHCI for antigen presentation remains as a pan-populational feature, synthesis of TNFα becomes restricted to a subset, even within adult central nervous system regions. Response heterogeneity is evident ex vivo, in situ, and in vivo, but is not limited to TNFα production or to TLR-triggered functions. Also, clearance activities for myelin under physiological and pathophysiological conditions, IFNγ-enforced upregulation of MHCII, or challenged inductions of other proinflammatory factors reveal dissimilar microglial contributions. Notably, response heterogeneity is also confirmed in human brain tissue. Our findings suggest that microglia divide by constitutive and inducible capacities. Privileged production of inflammatory mediators assigns a master control to subsets. Sequestration of clearance of endogenous material versus antigen presentation in exclusive compartments can separate potentially interfering functions. Finally, subsets rather than a uniform population of microglia may assemble the reactive phenotypes in responses during infection, injury, and rebuilding, warranting consideration in experimental manipulation and therapeutic strategies.

Impairment and Differential Expression of PR3 and MPO on Peripheral Myelomonocytic Cells with Endothelial Properties in Granulomatosis with Polyangiitis.

Background. Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are autoimmune-mediated diseases characterized by vasculitic inflammation of respiratory tract and kidneys. Clinical observations indicated a strong association between disease activity and serum levels of certain types of autoantibodies (antineutrophil cytoplasm antibodies with cytoplasmic [cANCA in GPA] or perinuclear [pAN CA in MPA] immunofluorescence). Pathologically, both diseases are characterized by severe microvascular endothelial cell damage. Early endothelial outgrowth cells (eEOCs) have been shown to be critically involved in neovascularization under both physiological and pathological condition. Objectives. The principal aims of our study were (i) to analyze the regenerative activity of the eEOC system and (ii) to determine mPR3 and MPO expression in myelo monocytic cells with endothelial characteristics in GPA and MPA patients. Methods. In 27 GPA and 10 MPA patients, regenerative activity blood-derived eEOCs were analyzed using a culture-forming assay. Flk-1(+), CD133(+)/Flk-1(+), mPR3(+), and Flk-1(+)/mPR3(+) myelomonocytic cells were quantified by FACS analysis. Serum levels of Angiopoietin-1 and TNF-α were measured by ELISA. Results. We found reduced eEOC regeneration, accompanied by lower serum levels of Angiopoietin-1 in GPA patients as compared to healthy controls. In addition, the total numbers of Flk-1(+) myelomonocytic cells in the peripheral circulation were decreased. Membrane PR3 expression was significantly higher in total as well as in Flk-1(+) myelomonocytic cells. Expression of MPO was not different between the groups. Conclusions. These data suggest impairment of the eEOC system and a possible role for PR3 in this process in patients suffering from GPA.

Cimicifuga racemosa and its triterpene-saponins prevent the Metabolic Syndrome and deterioration of cartilage in the knee joint of ovariectomized rats by similar mechanisms.

PURPOSE: An unphysiologic accumulation of fat cells in many parts of the body including abdomen and joints results in increased production of pro-inflammatory cytokines which have adverse effects on serum lipids, glucose and on joint cartilage. The special extract of Cimicifuga racemosa CR BNO 1055 was shown to reduce the size of the abdominal fat depot. It was therefore tempting to test whether this extract, its saponin and its unpolar and polar fractions S- and R-fraction respectively (no quotation) also reduce fat depots and fat cell accumulation in a fat depot located in the lower hind leg (called paratibial fat depot = PFD), in joint fat pads (in the knee joint this is called Hoffa's fat pad) that occur in response to ovariectomy and whether this was accompanied by reduced serum lipids, glucose and improved cartilage features in the knee joint. METHODS: Rats (n = 10/group) were ovariectomized (ovx) and fed with CR BNO 1055, S- or R-fraction containing food (average intake 8.2, or 2.05 or 7.07 mg/day/animal) for 4 weeks. Ovx rats kept under no additive-containing food served as controls. The sizes of the PFD, of Hoffa's fat pad and of the cartilage thickness of the knee joints were determined by quantitative computer tomography and histomorphometrically. In the serum cholesterol, leptin and glucose levels were measured. RESULTS: High load with fat tissue in the PFD and in the knee joints was present in the ovx rats. Treatment with CR BNO 1055 and its S-fraction reduced fat load of both, Hoffa's fat pad and of the PFD significantly and this resulted in reduced body weight which was significant under CR BNO 1055. Fat load in the PFD correlated significantly with the height of serum leptin and cholesterol. The fat load in the knee joint correlated inversely with the size of knee cartilage tissue. CONCLUSIONS: High fat load of the body increases following ovx and this causes increased serum leptin, cholesterol and glucose levels. Following ovx the size of Hoffa's fat pad increases also significantly and this has adverse effects on knee cartilage tissue. Therefore, increased fat tissue in joints appears to belong to the Metabolic Syndrome. This effect can be largely prevented by CR BNO 1005 and its S- but not by its R-fraction. Hence, the saponins in CR BNO 1055 may be useful in preventing the Metabolic Syndrome and osteoarthritis.

Light-emitting diodes in modern microscopy--from David to Goliath?

Proper illumination is essential for light microscopy. Whereas in early years incandescent light was the only illumination, today, more and more specialized light sources, such as lasers or arc lamps are used. Because of the high efficiency and brightness that light-emitting diodes (LED) have reached today, they have become a serious alternative for almost all kinds of illumination in light microscopy. LED have a high durability, do not need expensive electronics, and they can be switched in nanoseconds. Besides this, they are available throughout the UV/Vis/NIR-spectrum with a narrow bandwidth. This makes them ideal light sources for fluorescence microscopy. The white LED, with a color temperature ranging from 2,600 up to 5,000 K is an excellent choice for bright-field illumination with the additional advantage of simple brightness adjustments without changing the spectrum. This review discusses the different LED types, their use in the fluorescence microscope, and discusses LED as specialized illumination sources for Förster resonance energy transfer and fluorescent lifetime imaging microscopy.

A TNF-regulated recombinatorial macrophage immune receptor implicated in granuloma formation in tuberculosis.

Macrophages play a central role in host defense against mycobacterial infection and anti- TNF therapy is associated with granuloma disorganization and reactivation of tuberculosis in humans. Here, we provide evidence for the presence of a T cell receptor (TCR) αß based recombinatorial immune receptor in subpopulations of human and mouse monocytes and macrophages. In vitro, we find that the macrophage-TCRαß induces the release of CCL2 and modulates phagocytosis. TNF blockade suppresses macrophage-TCRαß expression. Infection of macrophages from healthy individuals with mycobacteria triggers formation of clusters that express restricted TCR Vß repertoires. In vivo, TCRαß bearing macrophages abundantly accumulate at the inner host-pathogen contact zone of caseous granulomas from patients with lung tuberculosis. In chimeric mouse models, deletion of the variable macrophage-TCRαß or TNF is associated with structurally compromised granulomas of pulmonary tuberculosis even in the presence of intact T cells. These results uncover a TNF-regulated recombinatorial immune receptor in monocytes/macrophages and demonstrate its implication in granuloma formation in tuberculosis.

Endothelial progenitor cells (EPC) in sepsis with acute renal dysfunction (ARD).

INTRODUCTION: Sepsis is characterized by systemic microvascular dysfunction. Endothelial progenitor cells (EPCs) are critically involved in maintaining vascular homeostasis under both physiological and pathological conditions. The aim of the present study was to analyze the endothelial progenitor cell system in patients suffering from sepsis with acute renal dysfunction. METHODS: Patients with newly diagnosed sepsis were recruited from the ICU in a nonrandomized prospective manner. Blood samples were obtained within the first 12 hours after the diagnosis of sepsis. For quantifying endothelial progenitor cells (EPCs), CD133+/Flk-1+ cells were enumerated by cytometric analysis. Analysis of EPC proliferation was performed by a colony-forming units (CFU) assay. Blood concentrations of proangiogenic mediators were measured by ELISA. Acute renal dysfunction was diagnosed according to the Acute Kidney Injury Network (AKIN) criteria. Depending on the overall mean creatinine concentration during the stay at the ICU, patients were either assigned to a 'normal creatinine group' or to a 'high creatinine group'. Survival rates, frequency of dialysis, the simplified acute physiology score (SAPS) II scores, and different laboratory parameters were collected/used for further clinical characterization RESULTS: Circulating EPCs were significantly higher in all sepsis patients included in the study as opposed to healthy controls. Patients within the 'high creatinine group' showed an even more pronounced EPC increase. In contrast, EPC proliferation was severely affected in sepsis. Neither total circulating EPCs nor EPC proliferation differed between patients requiring dialysis and patients without renal replacement therapy. Cell numbers and cell proliferation also did not differ between surviving patients and patients with sepsis-related death. Serum levels of vascular endothelial growth factor (VEGF), stromal derived factor-1 (SDF-1), and Angiopoietin-2 were higher in sepsis than in healthy controls. Sepsis patients within the 'high creatinine group' showed significantly higher mean serum levels of uric acid. CONCLUSIONS: Sepsis significantly affects the endothelial progenitor cell system, as reflected by increased EPC numbers, increased concentrations of proangiogenic mediators, and reduced proliferative capacity of the cells. This occurs independently from the frequency of dialysis and from patient survival. Increased serum levels of uric acid are possibly responsible for stronger EPC mobilization in sepsis patients with higher average creatinine levels.

The effects of 20-hydroxyecdysone and 17ß-estradiol on the skin of ovariectomized rats.

OBJECTIVE: 20-hydroxyecdysone has numerous favorable effects on a variety of organs, including the skin, where it improves wound healing. It is devoid of estrogenic and androgenic effects. Therefore, application of 20-hydroxyecdysone might be a new approach to improve skin conditions in postmenopausal women, and this was investigated in ovariectomized (OVX) rats. METHODS: After ovariectomy, rats received Ecd (18, 57, or 116 mg/animal/day) or 17ß-estradiol (E2)-3-benzoate (60 µg/kg body weight) in food for 12 weeks, and skin samples were evaluated histologically to quantify two dermal layers, the subcutaneous fat and muscle layers. RESULTS: Epidermal thickness was lowest in the OVX animals, slightly higher in the E2-treated animals, and significantly higher in the Ecd-treated animals. Dermal thickness was lowest in the intact and E2-treated animals and highest in the Ecd-treated animals. The subcutaneous fat layer was thickest in the OVX animals, thinner in the intact animals, and intermediate in the Ecd-treated animals. The muscle layer was smallest in the OVX and intact animals and significantly larger in the E2- and Ecd-treated animals. The number of proliferating cell nuclear antigen antibody-positive cells was lowest in OVX controls and significantly higher in all other groups. CONCLUSIONS: The Ecd-induced increases in epidermal and dermal thickness are suggestive of functional changes of the skin. The decreased amounts of subcutaneous fat in the E2- and Ecd-treated animals point to either a fat catabolic or an antianabolic effect. The ovariectomy-induced decrease in subcutaneous musculature was prevented by Ecd but not by E2. The stimulatory effects of Ecd on epidermal and dermal thickness and the muscle-increasing effects in the skin of OVX rats may indicate functional changes of the skin.

Advances in cellular, subcellular, and nanoscale imaging in vitro and in vivo.

This review focuses on technical advances in fluorescence microscopy techniques including laser scanning techniques, fluorescence-resonance energy transfer (FRET) microscopy, fluorescence lifetime imaging (FLIM), stimulated emission depletion (STED)-based super-resolution microscopy, scanning confocal endomicroscopes, thin-sheet laser imaging microscopy (TSLIM), and tomographic techniques such as early photon tomography (EPT) as well as on clinical laser-based endoscopic and microscopic techniques. We will also discuss the new developments in the field of fluorescent dyes and fluorescent genetic reporters that enable new possibilities in high-resolution and molecular imaging both in in vitro and in vivo. Small animal and tissue imaging benefit from the development of new fluorescent proteins, dyes, and sensing constructs that operate in the far red and near-infrared spectrum.

Expression and function of the C-class chemokine lymphotactin (XCL1) in Wegener's granulomatosis.

OBJECTIVE: In Wegener's granulomatosis (WG), vasculitic lesions are characterized by prominent infiltration of polymorphonuclear neutrophils (PMN) and T cells, but underlying pathogenic mechanisms remain to be defined. We analyzed the expression and functional role of the C-class chemokine lymphotactin, XCL1, in WG. METHODS: Sera and peripheral blood mononuclear cells (PBMC) were obtained from 16 patients with WG and healthy controls. Serum XCL1 concentrations were measured by ELISA. PBMC were subjected to flow cytometry for activation markers and immunophenotype of XCL1+ T cells. Renal biopsies were analyzed by double-label immunohistochemistry. In vitro stimulation of PMN with XCL1 was performed to study its function. RESULTS: Flow cytometry demonstrated coexpression of the activation markers CD25, CD69, and HLA-DR in a significantly higher proportion of T cells in WG patients in comparison to controls. XCL1 was found to be mainly expressed in CD4+CD28- T cells in WG patients. In renal biopsies, the presence of XCL1 was only detected within interstitial CD4+ and CD8+ T cells. Functional studies demonstrated a significant enhancement of IL-8 production in isolated PMN after in vitro stimulation with XCL1. There were no significant differences in XCL1 serum concentrations between WG patients and controls (p = 0.88). CONCLUSION: Our data indicated increased expression of XCL1 in CD4+ and CD8+ T cells in WG. Considering its function as a lymphocyte-specific chemoattractant, XCL1 might be a key modulator of T cell recruitment in WG. Functional studies further suggest that XCL1 may support vascular inflammation by induction of release of interleukin 8 in PMN.

LDL lipid apheresis rapidly increases peripheral endothelial progenitor cell competence.

BACKGROUND AND AIM: Endothelial progenitor cells (EPCs) have been shown to promote neovascularization under physiologic and pathologic conditions. Statins have been documented to increase the total number of circulating EPCs in long-term treated patients. Lipid apheresis is used to treat patient with refractory hyperlipidemia. The aim of our study was to evaluate whether lipid apheresis is associated with EPC mobilization. METHODS: Thirteen patients with refractory hyperlipidemia (analysis at the beginning and at the end of a single lipid apheresis treatment) and 10 healthy controls were included into the study. For quantifying total peripheral EPCs, CD133+/Flk-1+ myelo-monocytic blood cells were enumerated by flow cytometry. The proliferative potential of EPCs was evaluated by a "colony-forming unit" assay. In some patients, EPC eNOS expression was evaluated before and after treatment. RESULTS: Circulating EPCs and the cells' proliferative activity were lower in hyperlipidemia patients as compared to controls (0.14 +/- 0.07 vs. 0.6 +/- 0.14, P = 0.01, and 13.9 +/- 4.9 vs. 45.6 +/- 8.1, P = 0.0007). Lipid apheresis treatment was not associated with an increase in total EPCs. The cells' proliferative activity was strongly stimulated by lipid apheresis as reflected by an increase in the number of EPC colonies (13.9 +/- 4.9 to 34.1 +/- 7.3, P = 0.035). Analysis of EPC eNOS expression revealed a threefold increase in the cellular expression intensity after lipid apheresis. CONCLUSIONS: Patients with refractory hyperlipidemia exhibit lower peripheral EPC numbers and a lower proliferative activity of circulating EPCs than healthy controls. A single lipid apheresis treatment significantly stimulates EPC proliferation, it furthermore increases cellular eNOS. In summary, these results show that lipid apheresis mediates beneficial effects on the EPC system as an essential element in the process of vascular repair in the human organism.

Neural cell adhesion molecule expression on renal interstitial cells.

BACKGROUND: At early stages of kidney development, the neural cell adhesion molecule (NCAM) is highly expressed on cells of the metanephrogenic mesenchyme. During maturation of the fetal kidney, NCAM gradually disappears. So far, it has been widely accepted that NCAM in the adult kidney is only expressed by nerves, and not by other cell types. METHODS: NCAM expression was analysed in human adult healthy and diseased kidneys by immunohistochemistry and western blot analysis. NCAM+ renal interstitial cells were further characterized by double immunofluorescent staining using antibodies against neurofilaments, alpha smooth muscle actin, vimentin, alpha5beta1 integrin, CD68, CD11c, HLA-DR and the potential progenitor cell markers CD34, CD117, CD133, CD24, nestin and cadherin-11. RESULTS: In adult human kidneys, NCAM expression is restricted to rare interstitial cells with dendritic morphology, which are neurofilament-negative and predominantly localized on the corticomedullary junction. They are also negative for fibroblast cell markers, but co-express the haematopoietic stem cell markers CD34 and CD133. The number of NCAM+ interstitial cells increased in the initial phases of interstitial fibrosis. Western blot analysis of renal tissues with incipient interstitial fibrosis tissues showed the expression of the 140 kDa NCAM isoform. CONCLUSIONS: These data indicate that a rare subpopulation of NCAM+ interstitial cells could represent renal progenitors, and that NCAM+ interstitial cells can participate in the initial phase of interstitial fibrosis.

In vitro photodynamic therapy of childhood rhabdomyosarcoma.

Treatment of childhood rhabdomyosarcoma is limited by recurrent disease and the development of multidrug resistance. Therefore, novel treatment options are desirable. Photodynamic therapy (PDT) using the photodynamic agent hypericin is proposed as an alternative approach for intraoperative visualization and treatment of this disease. The aim of this study was to investigate in vitro effects of hypericin on childhood rhabdomyosarcoma and to evaluate photodynamic therapy as a possible basis for treatment. Rhabdomyosarcoma cells and fibroblasts (control) were incubated with increasing concentrations of hypericin. in vitro uptake and visualization of hypericin was evaluated by fluorescence microscopy and FACS. For photodynamic therapy, cells were exposed to white light for different time periods. Cytopathologic effects were assessed using standard histology. Cancer cells were investigated for cell viability (MTT assay), proliferative activity (Ki-67 assay), and apoptosis (TUNEL test). A 100% uptake of hypericin was found within the population of rhabdomyosarcoma cells. Uptake of hypericin in the fibroblasts was much less than in rhabdomyosarcoma cells. Hypericin without exposure to white light had no effect on tumor cell viability. After irradiation, PDT resulted in a nearly complete inhibition of cell proliferation of rhabdomyosarcoma cells with a corresponding increase in the frequency of apoptosis. In fibroblasts, PDT was less effective compared to tumor cells. Our data suggest hypericin as a novel tool for visualization and photodynamic therapy of childhood rhabdomyosarcoma.